• Energy Research

AbstractRegardless of where they are in the world, people depend on a reliable and sufficient supply of domestic hot water (DHW) for daily use. Some countries that have district heating (DH) infrastructure, such as Denmark and China, combine spacing heating (SH) and DHW together, with the aim of having a smart, energy efficient and environmentally friendly energy-consumption system. Nevertheless, the development of centralized DHW (CDHW) systems in these two countries differs significantly. This article details the challenges China's CDHW system is currently encountering and proposes to apply the flat station concept to improve China's CDHW system. Meanwhile, the technical advantages of the Danish CDHW, which would benefit China, are analyzed. Overall, from a technical point of view, the flat station concept is not only in line with China's current DH conditions but would compensate for some technical defects of the existing CDHW system.

The transition toward greener district heating (DH) systems is supported by the low-temperature operation of building heating systems. In addition to reducing the DH supply temperature it is necessary to parallelly decrease the DH return temperature. A common bottleneck in lowering DH return temperatures are multi-apartment buildings operating with domestic hot water (DHW) circulation loops. The most common substation design in existing systems heat the DHW circulation using the DHW heat exchanger (HEX). However, as the DHW circulation return temperature is high and the DHW circulation energy demand is relatively high as well, it often results in high DH return temperatures from the building. To address this challenge, this study investigated an innovative design for future-proof DHW substations for large multi-apartment buildings. In the new design, the DHW and DHW circulation loop are decoupled, each utilizing a dedicated HEX for its specific purpose. This new design enables aftercooling the high DH return temperature from the DHW circulation by channeling all, or part, of the return water through the space heating HEX. For the building case examples presented in this study, the DH return temperature reduction potentials are in the range of 5.4 °C–8.3 °C for the 4G temperature profiles.

Fourth-generation district heating (4GDH) has been used as a label or expression since 2008 to describe a transition path for decarbonization of the district heating sector and was defined in more detail in 2014. During recent years, several papers have been published on a concept called fifth generation district heating and cooling (5GDHC). This article identifies differences and similarities between 4GDH and 5GDHC regarding aims and abilities. The analysis shows that these two are common not only in the overarching aim of decarbonization but that they also to some extent share the five essential abilities first defined for 4GDH. The main driver for 5GDHC has been a strong focus on combined heating and cooling, using a collective network close to ambient temperature levels as common heat source or sink for building-level heat pumps. It is found that 5GDHC can be regarded as a promising technology with its own merits, yet a complementary technology that may coexist in parallel with other 4GDH technologies. However, the term “generation” implies a chronological succession, and the label 5GDHC does not seem compatible with the established labels 1GDH to 4GDH.

Abstract Projects like the 4DH research platform and Heat Roadmap Europe have successfully demonstrated that district heating is the only viable solution to efficiently utilize both low-grade renewable energy, excess heat from other sources as well as waste heat for providing heat for space heating and domestic hot water purposes. Nevertheless, there are open questions regarding cost competitiveness of district heating in combination with low energy buildings of the future. In fact, one of the challenges district heating is facing, is the general perception that district heating is too investment intensive compared to individual solutions. In many cases that perception is also used to imply that district heating has no future with the introduction of strict building energy codes that require new buildings to fulfill low energy buildings standards. In this paper, the levelized cost of heating using district heating and individual heating solutions are compared by looking at a concrete area where both the heat demand per square meter as well as the distance between buildings are varied. This study thus analyses when a 4th generation district heating system is competitive, under different linear heat densities.

Abstract For the last decades energy efficiency initiatives have avoided enormous amounts of energy consumption, to the favor of the environment and consumer expenditures. Although there is still a big potential for further energy efficiency improvements it is time to move further and start preparing the whole energy system for the challenge of oversupply from intermittent renewable energy sources, particularly in the power sector. In 2015 the maximum one-hour power oversupply from wind turbines alone in Denmark happened the 26th of June, peaking at around 900 MW and the oversupply over a 15-hour period was 10 GWh. Known solutions to make use of oversupply in the power sector are power export, energy storage and halting the power generation. The power export needs to rely on sufficient capacity at local interconnectors, power demand in the importing country and there is an economic gain in the export. Energy storages can range from storing of power in batteries, pumped hydro, synthetic fuels to fuel displacing at other energy sectors. The last option is stopping the turbines, which should be avoided. The optimum energy storage would have large capacity, fast charging, high recovery efficiency and low cost. Scoring high on all criteria’s can be difficult when focusing on a single energy sector. By widening the perspective and start taking advantages of synergies between the energy sectors there is a possibility to score high on all three criteria’s. In this paper the potential of utilizing synergies between the power and heat sectors will be explored by considering the projections for the Danish energy system in 2025. The result of the analysis shows the optimum energy storage of renewable power is achieved through fuel displacement in the heating sector in combination with utility sized heat pumps, electric boilers and large thermal storages.

Hydraulic unbalance is a common problem in Chinese district heating (DH) systems. Hydraulic unbalance has resulted in poor flow distribution among heating branches and overheating of apartments. Studies show that nearly 30% of the total heat supply is being wasted in Chinese DH systems due to a lack of pressure and flow control. This study investigated using pre-set radiator valves combined with differential pressure (DP) controllers to achieve hydraulic balance in building distribution systems, and consequently save energy and reduce the emissions. We considered a multi-storey building modelled in the IDA-ICE software, along with a self-developed mathematical hydraulic model to simulate its heat performance and hydraulic performance with various control scenarios. In contrast to the situation with no pressure or flow control, this solution achieves the required flow distribution and close-to-design room temperatures, as well as 16% heat savings, 74% pump electricity savings, and proper cooling of supply water. The energy consumption savings would therefore have positive environmental impacts, and be reflected in seasonal reductions of 2.1 kg/m2 CO2, 0.02 kg/m2 SO2, and 0.01 kg/m2 NO x for 3rd step energy efficiency buildings in Beijing.

AbstractRegardless of where they are in the world, people depend on a reliable and sufficient supply of domestic hot water (DHW) for daily use. Some countries, which have district heating infrastructure, combine spacing heating (SH) and DHW together, with the aim of having a smart, energy efficient and environmentally friendly energy-consumption system, such as Denmark and China. Nevertheless, the development of DHW networks in these two countries differs significantly. This article detailed the comparisons in technical aspect: common preparation methods of DHW through district heating was introduced in China and Denmark with the analysis on temperature level, hygienic situation of DHW system, circular system, flow capacity and heat metering.

Abstract For decades the focus of district heating (DH) has been on energy efficiency and minimum operating temperatures. This quest for continuous efficiency improvements led to the modern 4th generation of DH (4GDH), operating at lowest possible temperature for direct utilization by end-user. In recent years the term 5th generation DH (5GDH) has become popular for individual heat pump systems sharing thermal sources via uninsulated pipe network. While 5GDH has similarity with 4GDH it is a technically different solution, as the heat generation is moved to the end-users. When discussing 4GDH and 5GDH the focus quickly revolves about the efficiency of the distribution grid, however the discussion should be on the overall system efficiency and the levelized cost of the heat (LCOH). This paper analyzes LCOH for a mixed building area consisting of a central heat source, high or low energy buildings connected to 4GDH, 5GDH or a 4GDH variant with end-user temperature boosting for domestic hot water purposes. The analysis considers two countries: DK and UK. The analysis further explores the impact of the heat source temperature, from 10 °C to 60 °C, on the LCOH. The results indicate that 4GDH is the more competitive heat supply solution for the considered case.